OSU Extension Catalog

Pest identification

• Molluscs without shells; variable in size and coloring. (See Terrestrial Mollusc Tool for identification resources.)
• In Oregon, there are around 10 species of pest slugs (all of which are exotic, invasive species).

Biology and life cycle

• Most active in October, November, and late February to May, depending on moisture and temperature
• Generally not feeding December through early February (bait may be less effective during these times)
• Feeding on weeds, seeds, lichens, fungi, decaying vegetation, and other organic materials in Christmas tree fields
• Mating and egg laying occurs during active periods:
• Eggs are about 1 to 6 mm (1∕25 to 1⁄4") in diameter, round or oval, transparent, golden, or white (depending on the species).
• Eggs hatch after 2 to 4 weeks; those laid in October often overwinter until February.
• Possibility of overlapping generations

Growing years

• Look in weedy areas of the field.
• Scout around trees in the field in the evenings, early morning, or at night.
• Look in moist, protected areas during the day. Place pieces of plywood (2' × 2' or 3' × 3') in weedy areas and lift to find sheltering slugs; monitor population trends. (See Overview of Trapping and Monitoring Options.)
• Trap and scout after light rains and when night temperatures are above 50°F (10°C).
• Scout more actively during mild, wet winters or wet springs.

At harvest

• Look at interior of tree.
• Check in weedy areas of field, fencerows, etc.
• Monitor more intensively during wet periods.

Threshold

• Some trading partners, such as Hawaii and Japan, have zero tolerance for slugs.

Growing years

• Remove weeds wherever possible.
• Place bait in the spring and fall, when moisture is present and temperatures are above 50°F (10°C). Always review current label before use.
• Apply bait every 10 to 14 days when slugs are active; reapply if mold forms. Scout for slug mortality.
• Apply bait in growing and handling areas the year prior to harvest; apply following a spring rain.
• Apply bait evenly to the ground; do not pile bait.
• Encourage and conserve slug predators, such as ground beetles, by avoiding broad-spectrum insecticides.

At harvest

• Shake trees according to compliance agreements for destination countries. (See Best Management Practices at Harvest.)
• Limit the time trees touch the ground. Do not leave harvested trees on the ground overnight, if possible.
• Place trees on pallets to keep them off the ground at harvest.
• Apply slug bait around landing and loading areas following a rain.
• Do not put slug bait in containers—this is illegal. Also, slugs do not feed at 34°F (1°C) container temperatures.

Life cycle

Management